Mass flowering of Fagus crenata does not depend on the amount of stored carbohydrates in trees

Key messageStored carbohydrates in trees do not act as key requirements for mass flowering in a masting species, Fagus crenata.AbstractMany tree species exhibit high interannual variability in flower production at population level, called mass flowering. These species may need to store a certain amount of carbohydrate resources in trees for flowering. Based on this assumption, we hypothesized that masting tree species would blossom heavily when carbohydrates were sufficiently stored up in some specific organs. To test this hypothesis, we studied the relationship between stored carbohydrates in various organs just before the season of flower bud initiation and the number of flowers in the following year in a typical masting species, Fagus crenata (Fagaceae), over 10 years. In addition, we estimated the carbon accumulation period required for flower production by radiocarbon (C-14) contents of inflorescences in this species. During the study period, the individuals studied flowered synchronously about every 2 years, but levels of the flowering magnitude were different from each other. Total nonstructural carbohydrate (TNC) concentrations also exhibited large interannual variations, while the long-term trend of TNC over the 10-year observation period showed a general increase in all the investigated tree individuals. There was no significant relationship between the TNC concentrations in each organ and the number of flowers produced in the following year, including the massive flowering event in 2006 when all the selected trees flowered heavily. Fagus crenata produced inflorescences using carbon resources assimilated mainly in the year when the flower buds were formed. These results suggest that the storage of carbohydrate resources might not be a limiting factor in the occurrence or frequency of flowering in this species.